The invention relates to a drive device, comprising a tubular housing, on which a longitudinally moving movable unit is mounted, such unit having an inner part located in the interior of the housing and an outer part which is arranged externally on the housing and is magnetically coupled for movement with the inner part by means of a coupling means having at least one permanent magnet means.
Drive devices of this type, which are designed in the form of so-called rodless fluid power drive cylinders, are disclosed for example in the European patent publication 0 603 471 A1, the German patent publication (utility model) 1,982,379, the German patent publication 2,922,444 C2, the German patent publication (utility model) 8,230,298 or the German patent publication 2,207,126 B. Their inner part is designed in the form of a piston-like drive part able to be driven by fluid power in the longitudinal direction of the housing, whose motion is transmitted synchronously by the magnet coupling to the outer part, the latter being able to be connected with something to be moved. The coupling means comprises in each case inner and outer magnet means, which are made up of axially or radially permanently magnetized shaped parts and produce magnetic circuits, which pass through the wall of the housing at one or more points on the periphery.
Although known drive device are based on mature and reliable technology, the costs of manufacture are relatively high. Furthermore, attempts to reduce the overall size are hindered by there being a lower limit to the dimensions of the permanent magnets employed to provide the magnetic coupling force.
It is consequently one object of the present invention to provide a drive device of the type initially mentioned, which while having low costs of manufacture and compact dimensions produces high magnetic coupling forces.
In order to achieve this object there is the provision that the coupling means produces at least one magnetic circuit extending completely through the inner part and the housing, said magnetic circuit being closed by the outer part.
Whereas in the prior art the magnetic circuits produced by the coupling means at all times only partly extend through the housing and are limited to zones, which extend around the center of the housing, the coupling means of the invention produces at least one and if required several magnetic circuits, which completely pass through the housing and the input part athwart the longitudinal direction so that practically there is a diametral passage of a section of the magnetic circuit through the housing and the inner part. It has turned out that in the case of such an arrangement the permanent magnets employed are able to function at substantially better operating point so that there are larger coupling forces, which render possible a reduction in the volume of the magnet means and accordingly of the movable unit generally. Furthermore it is possible to utilize magnet means with a simple geometry, something which reduces the costs of production.
Further advantageous developments of the invention are defined in the dependent claims.
It is possible to so design the coupling means that at least one magnetic circuit produced by it extends only once through the inner part and the housing, the return taking place externally around part of the periphery of the housing via the outer part provided with components of the coupling means. It serves a good purpose in this connection inter alia for the outer part to be provided with a low-retentivity return connection part, same extending in the peripheral direction at least partially around the housing. It is here that more particularly a yoke-like is suitable, it being expedient for the entire outer part to be designed like a yoke with a U-like cross section so that same may be mounted in place quite conveniently from one longitudinal side of the housing and at the same time coupled with the inner part magnetically. The result is then more particularly simple handling in the course of assembly.
The coupling means may also be so designed that at least one magnetic circuit produced by it extends twice through the inner part and the housing so that therefore the return of the magnetic circuit takes place through the housing as well, but however with the opposite flux direction. In this case as well the outer part conveniently contributes to closing the magnetic circuit, it being an advantage for the inner part to have low-retentivity flux conducting bodies, arranged in the magnetic circuit, on the corresponding longitudinal sides of the housing.
Preferably the coupling device has a plurality of coupling units arranged in sequence in the longitudinal direction, such coupling units possessing mutually cooperating inner and outer magnet means. In this respect it is possible in a simple manner to set the desired magnetic coupling force by changing the number of coupling units.
It is particularly advantageous to provide each inner magnet means present with two inner magnet units, which are more particularly plate-like or rod-like and are arranged at a right angle to the longitudinal direction of the inner part adjacent to each other and are magnetized in the same direction for partaking in the formation of the magnetic circuit. These two magnet units may be inserted from the longitudinal side in mutually oppositely placed pockets in a magnet as part of the inner part, same attracting each other owing to the direction of magnetization selected. If then spacer means are provided, which are firmly connected with the inner magnet carrier, between the magnet units, there will be an automatic fixation in the position of the magnet units on the inner magnet carrier in the transverse direction thereof. It is then possible to do without complex design measures for attachment of the magnet unit. The intermediate space between the magnet units may if required be provided in addition with a low-retentivity flux conducting member so that a strong magnetic field is ensured.
A still further advantage of the drive device is that it renders possible the realization of the most various different cross sectional shapes of the tubular housing. Circularly round cross sectional forms are just as possible as configurations departing from a circular form to prevent relative twisting, as for instance oval and more particularly elliptical cross sections or elongated flat cross sections with flat longitudinal sides and arcuately rounded narrow sides.